Irvine, CA Environmental Rules: Flood Zones (2026)

Chapter 5-2 of the Irvine Zoning Ordinance establishes the FP-1 (Regulatory Floodway) and FP-2 (Area of Special Flood Hazard) districts covering land shown on FEMA's Flood Insurance Rate Maps and Flood Boundary and Floodway Maps, current copies of which are kept at the Public Works Department, One Civic Center Plaza. C. Section 5-2-24 sets the actual construction standards: residential lowest floors, including basements, must sit at least one foot above the base flood elevation (or, in an AO zone, one foot above the FIRM depth number, or two feet above grade if no depth number is listed), and enclosed areas below the lowest floor used only for parking, access, or storage must have flood vents totaling at least one square inch of net opening per square foot of enclosed area, with openings no higher than one foot above grade.

Nonresidential buildings may instead be floodproofed to be watertight, certified by a registered engineer or architect. Basements are prohibited outright for residential structures, including below-grade garages. In the FP-1 floodway, Section 5-2-22 bars landfills, new residential and nonresidential buildings, and any encroachment that would raise the base flood elevation, unless an engineer certifies no increase will result; farming, spreading grounds, and similar open uses are the only uses generally allowed. The Planning Commission may grant variances under Section 5-2-27 only on a showing of good cause and exceptional hardship, and never within a mapped regulatory floodway if the variance would raise flood levels.